View Full Version : Help with bending aluminum tubing
01-14-2006, 12:37 PM
OK, I need help. I have more experince bending steel than aluminum, and have run into a problem.
I have the Low-buck tubing bender.
I had used it on 1 1/4" .125 wall 6061T651 tubing and it worked great.
Now, I got the dies for 1 3/4" and tried to bend some 6061T6 (again, .125 wall thickness) and it does not bend, it breaks. As in "PUMP PUMP PUMP PUMP SNAP!"
Do I need a different temper? I am having a hard time understanding what is going on here. Is T651 that much more bendable than T6?
Thanks in advance for your help!
01-14-2006, 01:22 PM
Welcome to Metalmeet.
Jacin wrote:Now, I got the dies for 1 3/4" and tried to bend some 6061T6 (again, .125 wall thickness) and it does not bend, it breaks. As in "PUMP PUMP PUMP PUMP SNAP!"
I had the same problem bending 1.125" 6061T6 .125" wall tubing, it snapped.
I solved the problem by annealing the tubing. This most likely reduced the strength of the tubing but in my case it did not matter. Also, it was only about 10' of tubing, I wouldn't want to do a large bending job and have to anneal a lot of tubing.
Jacin wrote: Do I need a different temper? I am having a hard time understanding what is going on here. Is T651 that much more bendable than T6?
I guess the answer to your questions is yes. I'm no expert on all the different alloys and tempers, etc. I did look up TX51 in the Machinery's Handbook, reads: "stress-relieved by stretching", it goes on to list percentages for different types of material.
I have found sometimes it comes down to "availability" when procuring material for a particular job. What do I mean by that? Say you find out a particular alloy and temper of aluminum is ideal for a certain job but the only place or places you can buy it require a large minimum order or an amount not cost effective and prohibitive to getting the project complete? Doesn't work. Sometimes you have to "make do" with what you can get.
01-14-2006, 02:28 PM
6061 T6 is not recommended for forming unless it is annealed, which wil give it good formability. I have formed 6061 T-6 sheet in the past, and unless very generous corner rads are used it always breaks. You could anneal the tube with a torch, bend, and then heat treat it again.
01-14-2006, 10:29 PM
I was at a local shop that does a lot of tube bending, they were heating alum tubing to bend it. They said it would crack if they didn't.
01-15-2006, 05:03 AM
You didn't mention the centerline radius of the respective bends. Under the best conditions 1-3/4" tube can't be bent to anywhere near as small a radius as 1-1/4".
Give the bend radius and I'll look up the recommended minimum radius for T6 tubing in my Alcoa data book.
As has been suggested, try annealing the tubing in the bend area with a torch. By bringing it down to an "0" condition you'll be able to do a tigher bend radius. Bending will work harden the tube and bring it part way back to the T6 condition. After a couple of days the bent tube should age harden further so it might not be far off from it's pre-annealed properties.
01-15-2006, 08:58 AM
Thanks for all your input buys.
the centerline radius on the 1 3/4" dies is 7"
For the 1 1/4" it is 5"
I am going to try to anneal the tubing first.
Any suggestions to how to know it is annealed through?
Will the soot method work on tubin this tick-walled?
01-16-2006, 08:49 PM
The soot method should work. Try and heat slowly.
01-16-2006, 11:52 PM
Annealing heat-treated is a little trickier than say 3003 H14. The line between annealing it and melting it is finer. I would suggest you bend as you heat. That way you'll get a good feel as to how much heat is needed.
As stated, you'll remove most of the temper so you will need to re-temper if that is necessary for your application.
01-17-2006, 12:25 AM
As stated if you anneal it then let it sit it will age harden I have been told that within 30 days it should be fully hardened(opinion not fact). I would wonder if you heat treat after bending how much it might affect the shape as opposed to just letting it sit?
Any opinions/ data out there on age hardening results of this material?
01-17-2006, 10:16 PM
I have heard of the age hardening as well, but I dont recall if it was certain types or what, just remember hearing it and didn't believe it at first.
01-18-2006, 03:59 AM
Age hardening of heat treatable aluminum alloys like 6061 does happen.
From the Alcoa data book, 6061 will age harden to near full strength at room temperature in about a month although the majority of the hardening occurs in the first day. This data is after the material has been heat treated which consists of heating to a high temp, holding there for a length of time, then rapidly quenched. It's not clear on the progress of age hardening of annealed material.
Commercial heat treating can't wait 30 days or more to get full strength so they artificially age the material at a point above room temp to speed up the process.
I have a customer part that's deep drawn of 6061-0 (dead soft). After drawing it's heat treated. It's a high tolerance drawing process, the part needs to maintain roundness of .005"+/- on a 10" diameter. Distortion in the heat treat process makes the part quite a ways out of tolerance. To solve this, after the quench phase of the heat treatment the parts are stored in dry ice. The cold of the dry ice stops the age hardening. To bring the parts back into roundness tolerance they're put back into the drawing dies. After redrawing, the parts are allowed to come up to room temp and age harden naturally.
Now I'm curious about how much age hardening actually happens with material that's been torch annealed without the quench of heat treatment.
01-18-2006, 11:04 AM
I believe you'll get some age hardening after annealing but nothing close to the T6 condition. Heat treatment will be nessessary for that. If fact, every time you re-heattreat, you'll loose a little strength.
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